Cheap Memory Stick Duo Pro, perfect for Sony products especially the PSP! According to the site, guaranteed next day delivery too.
"These Sandisk branded 'Memory Stick Pro' cards are exactly the same spec as their Sony equivalents and fully compatible in any device using these cards.
Note: These cards have been 'factory refurbished' by Sandisk, which means the internal components have been thoroughly tested then refitted to new outer cases. The quality and lifespan is exactly the same as a new product, however they are supplied without retail packing and have either an 'R' or 'Refurb' marked on their casings."